screen.c

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/**************************************************************************************************************************************
* Project:       discoverpixy
* Website:       https://github.com/t-moe/discoverpixy
* Authors:       Aaron Schmocker, Timo Lang
* Institution:   BFH Bern University of Applied Sciences
* File:          common/gui/screen.c
*
* Version History:
* Date          Autor Email         SHA     Changes
* 2015-04-27    timolang@gmail.com  cf72baa Introduced a Screen (sub) module and divided app into multiple screens.
* 2015-04-27    timolang@gmail.com  77e6d0e Fixed screen implementation.
* 2015-05-10    timolang@gmail.com  b6ab7c8 Fixed compiler warning in tft and screen module.
* 2015-05-17    timolang@gmail.com  2d46336 Improved comments in implementation of button, checkbox, numupdown, tft, touch and screen modules/submodules.
* 2015-06-01    timolang@gmail.com  eb573bc Finalized calibration. Fixed a bug in screen module.
* 2015-06-06    timolang@gmail.com  c06661d Fixed some outdated comments in source code. Documented Gui Module in docu.
*
**************************************************************************************************************************************/

#include "screen.h"

/* The idea is as follows:
 * We only call screen callbacks from the gui_screen_update() method, which is called from the applications main loop.
 * Instructions to switch the screen will be delayed until the gui_screen_update() method is called again.
 * This makes it safe to change the screen from an touch interrupt (e.g. button callback)
 */

/* Possible Improvements:
 * Ensure that you can not navigate to a screen which is already in the history (because it will corrupt the list)
 */

static SCREEN_STRUCT* screen_list = NULL; //Head of the linked list which stores the screen history.
static SCREEN_STRUCT* screen_current = NULL; //Pointer to the current screen (= tail of the list)
static volatile SCREEN_STRUCT* screen_goto = NULL; //Screen we should navigate to once we enter the gui_screen_update() method again

SCREEN_STRUCT* gui_screen_get_current()
{
    return screen_current;
}


void gui_screen_update()
{
    if (screen_goto != NULL) { //we received the task to switch the screen
        SCREEN_STRUCT* go = (SCREEN_STRUCT*) screen_goto; //Backup volatile variable
        screen_goto = NULL; //reset the "goto instruction", since we're processing it now

        if (go->next != NULL) { //The screen is not the last in the list, so we're going back
            if (go->next != screen_current) { //this condition should always be false
                return; //list corrupted?
            }

            screen_current->on_leave(screen_current); //let the current screen free/unregister it's resources
            go->next = NULL; //remove the current screen from the list
        } else { //we're going forward (to a new screen)
            if (screen_current != NULL) { //this is not the first screen
                screen_current->on_leave(screen_current); //let the current screen free/unregister it's resources
                screen_current->next = go; //append the new screen to the end of the list
            } else { //first screen ever seen
                screen_list = go; //set the new screen as list-head
            }
        }

        go->on_enter(go); //let the new screen allocate/register it's resources
        screen_current = go; //the new screen is now the current screen. Transition done
    }

    if (screen_current != NULL) { //A screen has been set
        screen_current->on_update(screen_current); //Update current screen
    }
}



bool gui_screen_navigate(SCREEN_STRUCT* screen)
{
    if (screen == NULL || screen == screen_current || screen == screen_goto) { //invalid argument passed
        return false;
    }

    screen->next = NULL; //this will become the new tail of the list, so the next pointer must be NULL
    screen_goto = screen; //"send message" to main loop, to switch the screen
    return true;
}

bool gui_screen_back()
{
    if (screen_list == NULL) { //the list head is emtpy, nothing to go back to
        return false;
    }

    SCREEN_STRUCT* current = screen_list;
    SCREEN_STRUCT* last = NULL;

    //Find second last element in list
    while (current->next != NULL) {
        last = current;
        current = current->next;
    }

    if (last == NULL) {
        return false;    //There's only a single screen, there's no going back here
    }

    if (current != screen_current) {
        return false;    //The last entry in the list is not the current screen. List corrupted?
    }

    screen_goto = last; //"send message" to main loop, to switch the screen
    return true;
}